The present invention relates to a nozzle intended for the projection on to an object of a fluid, such as a gaseous flow, containing solid particles, particularly with a view to the fine, accurate and controlled scouring of surfaces. There are a multitude of types of surfaces to be scoured, some of which are relatively bulky, and in those cases rustic methods known for many years are sufficient.
Other surfaces, in contrast, require particular care and for these it is unsatisfactory to project irregular or very hard, or very harsh, or very soiling materials.
By way of example, human skin when treated for therapeutic or aesthetic purposes so as to remove the fine outer portion can be cited. The surface of works of art: painted canvas, plans and drawings, manuscripts and parchment, frescoes, sculptures made of wood or mineral materials, when painted or gilded, stained glass windows, porcelain, glazed earthenware, silver and gold plate, etc. together with the facades of buildings, particularly in order to remove deposits, patinas and the marks of time, soiling or graffiti, can also be cited.
A quite different field is the industrial one, where a multitude of cases are to be found requiring scouring, particularly for the purposes of restoration and cleaning.
By way of example, printing cylinders, which have a very finely engraved surface and have very small cells or channels that become loaded with ink and small impurities, require scrupulous cleaning that must both be comprehensive and also leave the printing surface intact.
Mention can also be made of aircraft structures, the bodywork of racing cars and, in general, any fragile or delicate structure that is coated with one or more layers of products that have to be removed subsequently, wholly or layer by layer, the latter condition assuming that it is possible to remove one layer without in any way encroaching on the one immediately below the preceding one.
There is a known projectable medium that lends itself particularly well to the scouring of delicate surfaces, namely a starchy polymer derived from wheat, which forms the subject-matter of U.S. Pat. No. 5,066,335.
This medium is projected with standard nozzles that have the drawback of creating an imprecise outlet flow, so that when carrying out the scouring of a large surface area in successive, juxtaposed parallel strips, each strip has a central zone that is completely scoured and irregular margins that make it necessary to create the adjacent strip by partly overlapping the neighbouring strip created previously. This makes it impossible to guarantee true accuracy since the lateral portion of the supplementary flow of medium can obviously lead to the scouring of missed points but also additional deep scouring of already scoured points, which can result in the lower layer being attacked.
The present invention makes it possible to create a flow of medium without irregular margins, which makes it possible to juxtapose the successive scoured strips in a rigorous manner, without any risk of irregularities and accidental attack of a layer that is to be presented in its complete integrity.
To this end, according to the present invention, there is provided a nozzle for the projection on to an object of a medium formed by fluid such as a gaseous flow containing solid particles, comprising a body through which there passes a longitudinal tubular passage, one end of which constitutes an inlet that has to be connected to the intake of a fluid supply conduit and the other end of which constitutes an outlet for the fluid that has passed through the nozzle, wherein the section of the tubular passage is variable between the inlet and the outlet, and said passage has three successive portions, which are:
an inlet chamber with a constant section,
an intermediate conduit with a variable section, the walls of which are convergent from the chamber to an oblong neck, which has a major axis and a minor axis and the area of which is equal to that of the circular section of the chamber, and
an outlet tube with a variable oblong section, the walls of which are divergent from the neck to an outlet orifice of oblong section having a major axis and a minor axis.
The invention may include any of the following features:
the inlet chamber has a circular section;
the oblong neck has two rectilinear edges, parallel to its major axis;
the oblong neck has two edges, which are more distant from each other in the central zone than at the sides of the neck;
each of the two edges is formed of at least two rectilinear segments;
the two edges are curved and joined to one another by lateral connecting neck mouldings;
the oblong neck has an elliptical section;
the oblong section of the outlet tube has two rectilinear edges parallel to its major axis;
the oblong section of the outlet tube has two edges, the spacing of which is greater in the central zone than at the sides of the tube;
each of the two edges is formed of at least two rectilinear segments;
the two edges are curved and joined to one another by lateral connecting neck mouldings;
the oblong section of the outlet tube has two edges, the spacing of which is greater at its sides than in its central zone;
the neck having an elliptical section, the oblong section of the outlet tube has two edges with the same curvature as those of the ellipse but of opposite convexity and joined to one another by lateral connecting neck mouldings;
the oblong section of the tube is enlarged laterally by two longitudinal channels;
the inlet chamber contains elements in relief constituting flow concentrators;
the outlet tube is determined by a water-and airtight wall through which there passes at least one passage intended to be connected to a source of gas containing ionised particles and opening out obliquely into said tube, in a downstream direction considering the direction of displacement of the fluid;
the source of gas is associated with a device for mobilisation at high speed;
the device for mobilising the gas is designed so as to impress thereon a speed higher than that of sound;
the gas contains two substantially equal fractions of ionised particles of inverse polarity;
the gas is slightly humid air.
Other characteristics of the invention will become apparent from the following detailed description given with reference to the attached drawing. The invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic view in longitudinal section of a nozzle in accordance with one embodiment of the invention;
FIGS. 2, 3 and 4 are diagrammatic views in cross section of the nozzle in FIG. 1, each positioned in line with the place where it is located;
FIG. 5 is a diagrammatic view in longitudinal section of the same nozzle, at 90xc2x0 to the section in FIG. 1;
FIGS. 6, 7 and 8 are diagrammatic views in cross section of the nozzle in FIG. 5, each positioned in line with the place where it is located;
FIG. 9 is a diagrammatic view in longitudinal section of a nozzle in accordance with another embodiment of the invention;
FIGS. 10, 11 and 12 are diagrammatic views in cross section of the nozzle in FIG. 9, each positioned in line with the place where it is located;
FIG. 13 is a diagrammatic view in longitudinal section of the same nozzle, at 90xc2x0 to the section in FIG. 9;
FIGS. 14, 15 and 16 are diagrammatic views in cross section of the nozzle in FIG. 13, each positioned in line with the place where it is located;
FIGS. 17, 19 and 21 show, in cross section of the nozzle, three variant forms of the oblong neck; and
FIGS. 18, 20 and 22 show three variant forms of the outlet orifice each corresponding to the shape of the oblong neck shown opposite, i.e. neck in FIG. 17 and outlet orifice in FIG. 18, neck in FIG. 19 and outlet orifice in FIG. 20, neck in FIG. 21 and outlet orifice in FIG. 22.